Pressure filters are commonly used to industrially process drainage for the purpose of environmental protection. Drainage containing sludge is processed by a pressure filter and separated into solid leach residue and water that is less muddy. Such dry leach residue occupies space much smaller than the drainage, and can be easily disposed through incineration or landfilling like normal waste. The solid-free water can be recycled, further processed and reused, or drained directly.
The existing pressure filter, when used, has its filter plates pressed together and wrapped by filter cloth. Closed space is formed between the filter cloth covering the adjacent filter plates. Then drainage is fed into the closed space through the central holes of the filter plates. Since the drainage comes with high pressure, water is pushed through the filter cloth and drained form the pressure filter through water channels formed inside the filter plates. On the other hand, sludge is blocked by the filter cloth, and accumulated in the closed space between the adjacent filter plates. Having the sludge being accumulated to a certain amount, once the filter plates are released, the sludge compressed into cakes can drop out the filter cloth between the filter plates. With more and more attention focused on environmental protection and energy conservation, pressure filters are increasingly popular as they can turn large-volume drainage into small-volume filter cakes, which means significantly reduced costs for drainage process and more economic and social advantages. It is clear through the foregoing process that efficiency and effectiveness are two major measures to assess a pressure filter. While the former refers to how many tons of drainage is processed by a given pressure filter in a given time period, the latter means how low the water content in the resultant filter cakes is. All improvements made for a pressure filter are about one or both of the issues.
All of the existing pressure filters are designed as having a single feed inlet. This makes the feed speed and in turn the working efficiency limited. In the recently developed large-sized pressure filters, the length of filtering section is significantly increased. As a result, in the process of filtering drainage, it is common that when the filter plate closer to the feed inlet has seen sludge dried and accumulated by gravity, the filter plate far away from the feed inlet have not received any sludge. This difference causes uneven pressing and may be responsible to premature wear of components.
Presently, most filter plates have a diameter below 0.6 m. Although an enlarged filter plate may be more productive of processed sludge, and even double the working efficiency, its larger diameter brings about some solid problems. First, the greater the diameter is, the longer the circumference is. This means it is more difficult to press adjacent filter plates into a reliable sealing condition. Particularly, after removal of filter cakes, there is always some residue sticking in the sealing structure between the filter plates. In practice, one pressure filter typically has about a dozen of heavy, bulky filter plates, and it is very likely that manual clean unintentionally misses some residue. However, such residue may prevent the sealing condition from forming between the filter plates. In this case, drainage with sludge will leak from the failed sealing structure directly and escape from the filter cloth. Secondly, the pressure acting on the filter plate is equal to the product of multiplying the pressure intensity of the drainage by the area of the filter plate. That means the greater the diameter of the filter plate is, the larger the pressure of drainage acting on the filter plate is. Thus, in the pressing and filtering process, each filter plate impacted by rush of drainage at its two sides tends to sway acutely. In the event that the filter plate is not strong enough, it will break and soon reach the end of its service life.